There are two categories of base materials for thermobinding interlinings: the textile base materials proper and the nonwovens. The textile base materials proper are obtained by weaving or knitting of yarns, while the nonwovens are obtained by formation and consolidation of a web of fibers or filaments.
The use of nonwovens as interlining base material presents advantages, particularly as regards production costs. There are nevertheless certain disadvantages, due in particular to their production method. Due to the fact that the fibers or filaments are deposited in web form, without there being any accurate control of the direction taken by the fibers or filaments throughout the width of the web, density differences and surface irregularities occur in the nonwoven. Also, because of the irregular distribution, directionwise, of the fibers or filaments, the nonwoven has insufficient dimensional stability: it can be irreversibly deformed under the effect of an extension, which, in the case of an interlining, causes a poor stabilization of the garment piece on which said nonwoven has been thermobonded.
In spite of their high cost price, the textile base materials proper are preferred in those applications where the aforesaid disadvantages presented by the nonwovens are redhibitory. The production method, by weaving or knitting, of such base materials, gives them the homogeneity, notably directionwise, lacking in the nonwovens.
In the field of thermobinding interlinings, the aim is also that the thermofusible polymer should not spread through inside the interlining base material, as this would locally rigidify the base material and, consequently, the garment piece. It is understandable that, for an equal weight, a given polymer diffuses through with all the more difficulty as the surface of the base material on which said polymer is deposited is dense, i.e. that the space between the various fibers or filaments constituting the base material is reduced. From a structural standpoint, for an equal weight, the nonwoven has a much denser surface than the textile base material.